feat(frontend): add API client, layout, and routing

- Create Axios-based API client with sources, jobs, and dashboard endpoints
- Add responsive Layout component with navigation sidebar
- Set up React Router with Dashboard, Backups, and Settings routes
- Configure TanStack Query provider with default options
- Use lucide-react for navigation icons

frontend/node_modules/lucide-react/dist/esm/icons/calendar-plus.js

@@ -0,0 +1,20 @@
+/**
+ * @license lucide-react v0.303.0 - ISC
+ *
+ * This source code is licensed under the ISC license.
+ * See the LICENSE file in the root directory of this source tree.
+ */
+
+import createLucideIcon from '../createLucideIcon.js';
+
+const CalendarPlus = createLucideIcon("CalendarPlus", [
+  ["path", { d: "M21 13V6a2 2 0 0 0-2-2H5a2 2 0 0 0-2 2v14a2 2 0 0 0 2 2h8", key: "3spt84" }],
+  ["line", { x1: "16", x2: "16", y1: "2", y2: "6", key: "m3sa8f" }],
+  ["line", { x1: "8", x2: "8", y1: "2", y2: "6", key: "18kwsl" }],
+  ["line", { x1: "3", x2: "21", y1: "10", y2: "10", key: "xt86sb" }],
+  ["line", { x1: "19", x2: "19", y1: "16", y2: "22", key: "1ttwzi" }],
+  ["line", { x1: "16", x2: "22", y1: "19", y2: "19", key: "1g9955" }]
+]);
+
+export { CalendarPlus as default };
+//# sourceMappingURL=calendar-plus.js.map